Silicon load and the development of diatoms in three river-lake systems in countries surrounding the Baltic Sea

We studied the formation of dissolved silicon loads from rivers to lakes, the development of diatoms in lakes and the role of climatic forcing on the silicon cycle in three river-lake systems in Sweden, Estonia and Northern Germany. We found coherent seasonality in the silicon loads of the two northern rivers, which was probably caused by the common snow-type hydrology of the catchments as distinct from the rain-type hydrology of the catchment, further south. The similarity among lakes in the dynamics of the Si-related variables studied resulted from similarities in mean lake depth and mixing type rather than the climatic regime. Among the variables measured at the three sites, river water discharge responded most coherently to climatic forcing as synchronized by the North Atlantic Oscillation winter index (NAOw). Water discharge and Si load were strongly linked variables and showed coherent patterns among the river systems. We found significant season-specific correlations of the NAOw with either the biomass or the share of diatoms in each lake, but no coherent pattern among the lakes. Our results indicate that processes driven by water discharge are more coherent across regions than in-lake processes.     

Choice of scan-sampling intervals—An example with quantifying neighbours in dairy cows

To date, only a few studies using scan-sampling intervals to record neighbours in groups of animals explain how the interval length was chosen. In this study, we investigated the effects of different scan-sampling intervals, behavioural context, and the definition of neighbours on the accuracy of data as compared to a quasi-continuous observation. The data was collected from dairy cows kept in cubicle housing systems. Dairy herds of 22–43 cows on 6 farms were observed once a minute with an automatic tracking system for 6 days, and both the nearest neighbour and all neighbours within a defined distance of each cow were recorded with references to the activity, feeding and lying area and stored in neighbourship matrices. In the analysis, we used data collected at intervals of 2, 3, 4, …, 30 min, and correlated this simulated data with the data based on the 1-min interval using a specialised correlation coefficient for matrices τ_Kr. This correlation coefficient was then used as the response variable in mixed-effects models. We found that the size of the correlation coefficients generally decreased as interval length increased. This decrease was less pronounced for all neighbours than for the nearest neighbour. Moreover, the decrease was greatest with data from the activity area and lowest with data from the lying area. We concluded that, even with the relatively slow dairy cows in a barn environment, neighbour recordings should be conducted at short scan-sampling intervals in order to achieve a minimum correlation of τ_Kr = 0.8 with the quasi-continuous data. Intervals of every 2, 8 and 17 min are recommended for observation of neighbours in dairy cows for the activity, feeding and lying areas, respectively, and species that move faster may well require even shorter sampling intervals.     

Differences between single and paired heifers in residency in functional areas, length of travel path, and area used throughout days 1–6 after integration into a free stall dairy herd

The integration of heifers into free stall dairy herds is a frequent management procedure, but little systematic research has been conducted on its effect on cow behavior. Previous studies mainly focused on aggressive interactions, but it is also of interest how integration affects the spatial distribution of both the cows in the herd and the integrated heifers. In the present study we integrated a single and a pair of heifers on each of six Swiss working farms in a balanced order. Using an automatic tracking system, we recorded the positions of all the cows and of the integrated heifers at 1 min intervals for six continuous 24 h periods. From these data we calculated the proportion of time the animals spent in the activity area, at the feed rack and in the lying cubicles, their average path length and the area of the barn that they used. We then compared the behavior of the integrated heifers with that of the cows in the introductory weeks. We also compared the behavior of the cows recorded in the control weeks directly preceding the integration and in the introductory weeks. For evaluation we used linear mixed-effects models. Singly integrated heifers spent a higher proportion of time in the activity area (0.29 vs. 0.14; P < 0.001) and a lower proportion of time in the lying area (0.40 vs. 0.53; interaction with day, P = 0.011) than the cows, whereas the heifers of the pairs mainly spent a lower proportion of time in the feeding area than the cows (0.23 vs. 0.32; interaction with day, P = 0.044). Average path length was longer for the integrated heifers soon after introduction but approached the values of the cows later on (interaction with day, P = 0.012). The total barn area used by a given animal was largest in the cows and was reduced in heifers integrated singly or in pairs (cows: 341/373 m², pairs: 306 m², single heifer: 333 m²; P = 0.055). Cows were little influenced in their space use by the integration of a single or pair of heifers. In summary, the behavior of the singly integrated heifers differed more markedly from that of the cows than the behavior of the heifers introduced in pairs during the introductory week. We would therefore recommend integrating pairs rather than single heifers into herds of dehorned dairy cows to ease their integration.     

Controls of dissolved organic matter quality: evidence from a large‐scale boreal lake survey

Inland waters transport large amounts of dissolved organic matter (DOM) from terrestrial environments to the oceans, but DOM also reacts en route, with substantial water column losses by mineralization and sedimentation. For DOM transformations along the aquatic continuum, lakes play an important role as they retain waters in the landscape allowing for more time to alter DOM. We know DOM losses are significant at the global scale, yet little is known about how the reactivity of DOM varies across landscapes and climates. DOM reactivity is inherently linked to its chemical composition. We used fluorescence spectroscopy to explore DOM quality from 560 lakes distributed across Sweden and encompassed a wide climatic gradient typical of the boreal ecozone. Six fluorescence components were identified using parallel factor analysis (PARAFAC). The intensity and relative abundance of these components were analyzed in relation to lake chemistry, catchment, and climate characteristics. Land cover, particularly the percentage of water in the catchment, was a primary factor explaining variability in PARAFAC components. Likewise, lake water retention time influenced DOM quality. These results suggest that processes occurring in upstream water bodies, in addition to the lake itself, have a dominant influence on DOM quality. PARAFAC components with longer emission wavelengths, or red‐shifted components, were most reactive. In contrast, protein‐like components were most persistent within lakes. Generalized characteristics of PARAFAC components based on emission wavelength could ease future interpretation of fluorescence spectra. An important secondary influence on DOM quality was mean annual temperature, which ranged between ?6.2 and +7.5 °C. These results suggest that DOM reactivity depends more heavily on the duration of time taken to pass through the landscape, rather than temperature. Projected increases in runoff in the boreal region may force lake DOM toward a higher overall amount and proportion of humic‐like substances.     

CO2 evasion from boreal lakes: Revised estimate,drivers of spatial variability,and future projections

Lakes (including reservoirs) are an important component of the global carbon (C) cycle, as acknowledged by the fifth assessment report of the IPCC. In the context of lakes, the boreal region is disproportionately important contributing to 27% of the worldwide lake area, despite representing just 14% of global land surface area. In this study, we used a statistical approach to derive a prediction equation for the partial pressure of CO₂ (pCO₂) in lakes as a function of lake area, terrestrial net primary productivity (NPP), and precipitation (r² = .56), and to create the first high‐resolution, circumboreal map (0.5°) of lake pCO₂. The map of pCO₂ was combined with lake area from the recently published GLOWABO database and three different estimates of the gas transfer velocity k to produce a resulting map of CO₂ evasion (FCO₂). For the boreal region, we estimate an average, lake area weighted, pCO₂ of 966 (678–1,325) μatm and a total FCO₂ of 189 (74–347) Tg C year^?1, and evaluate the corresponding uncertainties based on Monte Carlo simulation. Our estimate of FCO₂ is approximately twofold greater than previous estimates, as a result of methodological and data source differences. We use our results along with published estimates of the other C fluxes through inland waters to derive a C budget for the boreal region, and find that FCO₂ from lakes is the most significant flux of the land‐ocean aquatic continuum, and of a similar magnitude as emissions from forest fires. Using the model and applying it to spatially resolved projections of terrestrial NPP and precipitation while keeping everything else constant, we predict a 107% increase in boreal lake FCO₂ under emission scenario RCP8.5 by 2100. Our projections are largely driven by increases in terrestrial NPP over the same period, showing the very close connection between the terrestrial and aquatic C cycle.     

Regional Variability and Drivers of Below Ice CO<Subscript>2</Subscript> in Boreal and Subarctic Lakes

Northern lakes are ice-covered for considerable portions of the year, where carbon dioxide (CO₂) can accumulate below ice, subsequently leading to high CO₂ emissions at ice-melt. Current knowledge on the regional control and variability of below ice partial pressure of carbon dioxide (pCO₂) is lacking, creating a gap in our understanding of how ice cover dynamics affect the CO₂ accumulation below ice and therefore CO₂ emissions from inland waters during the ice-melt period. To narrow this gap, we identified the drivers of below ice pCO₂ variation across 506 Swedish and Finnish lakes using water chemistry, lake morphometry, catchment characteristics, lake position, and climate variables. We found that lake depth and trophic status were the most important variables explaining variations in below ice pCO₂ across the 506 lakes_. Together, lake morphometry and water chemistry explained 53% of the site-to-site variation in below ice pCO₂. Regional climate (including ice cover duration) and latitude only explained 7% of the variation in below ice pCO₂. Thus, our results suggest that on a regional scale a shortening of the ice cover period on lakes may not directly affect the accumulation of CO₂ below ice but rather indirectly through increased mobility of nutrients and carbon loading to lakes. Thus, given that climate-induced changes are most evident in northern ecosystems, adequately predicting the consequences of a changing climate on future CO₂ emission estimates from northern lakes involves monitoring changes not only to ice cover but also to changes in the trophic status of lakes.     

Diel Surface Temperature Range Scales with Lake Size

Ecological and biogeochemical processes in lakes are strongly dependent upon water temperature. Long-term surface warming of many lakes is unequivocal, but little is known about the comparative magnitude of temperature variation at diel timescales, due to a lack of appropriately resolved data. Here we quantify the pattern and magnitude of diel temperature variability of surface waters using high-frequency data from 100 lakes. We show that the near-surface diel temperature range can be substantial in summer relative to long-term change and, for lakes smaller than 3 km², increases sharply and predictably with decreasing lake area. Most small lakes included in this study experience average summer diel ranges in their near-surface temperatures of between 4 and 7°C. Large diel temperature fluctuations in the majority of lakes undoubtedly influence their structure, function and role in biogeochemical cycles, but the full implications remain largely unexplored.     

Considerations on the flow configuration of membrane chromatography devices for the purification of human basic fibroblast growth factor from crude lysates

Membrane chromatography possesses numerous advantages such as operation at high flow rates, low back pressure, ease of handling and scale up, which make the membrane adsorber process a viable alternative to conventional packed column chromatography. A purification process for the isolation of human recombinant basic fibroblast growth factor (FGF‐2) based on membrane chromatography was investigated using devices with different flow configurations. In the first process, the FGF‐2 capture step was performed with an axial flow device, while the alternative method achieved direct capture of FGF‐2 from unclarified cell lysate with a tangential flow device. In both processes, FGF‐2 purities exceeded 82% and the purified cytokine displayed high biological activity. Binding capacity (BC) from fermentation broth of the axial flow device was 28 mg/mL. This was 50% higher than the BC obtained with the tangential flow device under particle‐free supernatant conditions (18 mg/mL) and 150% higher compared to the BC achieved with unclarified cell lysate (11 mg/mL). While membrane chromatography in tangential flow mode omits clarification and thus reduces the number of stages in the downstream process, it displays lower peak resolution and leads to a lower overall process yield.     

Licht- und elektronenmikroskopische Studien über die Fasergliastruktur der Epiphysen-Subcommissuralregion der Primaten

Zusammenfassung Bei Cebus, Ateles, Macaca und Pan wird die Gliaarchitektonik der Commissura posterior, des Subcommisuralkomplexes und der angrenzenden Rec. mesocoelicus und Rec. pinealis beschrieben. In allen diesen Abschnitten sind sowohl im Verlauf als auch in der Anordnung der Faserglia Gesetzmäßigkeiten zu erkennen. In der Commissura posterior finden sich gebündelte Radiärfasern, deren Endfüße die Pia mater durchsetzen. Kurze Faserbündel sind für die subependymale Gliafaserdeckschicht des Recessus pinealis und für die Fasergliatextur des Epiphysenparenchyms charakteristisch. In der subependymalen Gliaschicht des Subcommissuralorgans herrscht ein feines, füzartiges Gliafaserwerk vor, das um die in die Tiefe dringenden Ependymkanälchen (Ateles) eine besonders dichte Formation ausbildet. Die Tatsache, daß sekretorisch aktive Partien des Subcommissuralorgans von einem auffallend dichten Gliafasergeflecht eingehüllt werden, spricht gegen eine Behinderung des Stoffaustausches durch die innere Gliafaserdeckschicht. Elektronenmikroskopische Befunde zeigen, daß sowohl in diesen Ausläufern der Faserastrocyten als auch in den entsprechenden perivasculären Fasergliaformationen ein Fortsatzprofil nie vollständig von Gliafilamenten ausgefüllt wird.

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Light and electron microscopic studies on the structure of fibrous astroglia in the pineal-subcommissural region of primates

Summary In Cebus, Ateles, Macaca, and Pan, the fibrous neuroglia of the posterior commissure, the subcommissural complex and the adjoining recessus (Rec. mesocoelicus, Rec. pinealis) show definite organizational and structural features. In the posterior commissure, fiber bundles course radially and fiber end-feet terminate in the Pia mater. Neuroglia in the subependymal fiber layer of the Recessus pinealis and fibrous astroglia in the Epiphysis cerebri have characteristically short fiber bundles. In the subependymal glial layer of the subcommissural complex, fibrous astroglia forms a dense felt-like network around ependymal channels (Ateles). The dense network of neuroglial fibers surrounding the secretorily-active parts of the subcommissural complex suggests that metabolic exchange through the inner fibrous neuroglial layer is not hindered. Electron microscopy indicates that the processes of the fibrous astrocytes as well as of the corresponding perivascular formations of fibrous neuroglia are not entirely filled with glial filaments.

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Herrn Prof. Dr. Dr. E. Horstmann, Hamburg, gewidmet.

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Mit Unterstützung durch die Deutsche Forschungsgemeinschaft. Herrn Prof. Dr. H. Hofer, Delta Primate Center, Covington, La., USA, früher Frankfurt a. M., danke ich für das Interesse, das er dieser Studie entgegengebracht hat.